In the past, an unlocking structure, for example for a car, has been proposed in which a key, functioning as an operation member, has first and second thru-hole rows formed along its longitudinal direction. The first thru-hole row causes the generation of a first encoded pulse train and the second thru-hole row causes the generation of a second encoded pulse train. The first pulse train and the second pulse train are generated when the key is inserted into a key hole having paired light projecting and light receiving elements arranged correspondingly to the first thru-hole row and the second thru-hole row. The second encoded pulse train is read out by treating the generated first pulse train as a synchronizing signal. If the read-out second encoded pulse train agrees with the pre-set encoded signal an unlocking action of a door is performed.
According to the foregoing conventional structure, however, because the first pulse train is employed only as a synchronizing signal, the encoded signal may be obtained only from the second pulse train. Thus, the number of encoded signal pulses is reduced in comparison to the actual number of thru-holes formed in the key.
Further, the unlocking action can not be performed if the first and second thru-hole rows are not alighed with, and read out by, the corresponding first and second readers. That is, the arrangement is inconvenient because the unlocking device does not operate if the key is inserted upside down.